Hi Sally,
Maybe I should know better than to answer mails before coffee,
but I see a conflict in your statements.
On one hand you say Fab house editing is normal for results that
are desirable, and then you add a note saying they can't do it
without your consent.
So,
Do they call you on every single build to get your consent?
even for adding thieving and etching compensation?
Or
Is it more "normal" for the fab house to make the edits anyway and not
bother you, since they know what you meant?
also, (not intending to sound critical, but) just friendly advice that maybe
your second note should be revised to include an actual IPC document
Rework per IPC WHAT?
nice to hear from you again!
Jack
p.s. thinking about these notes reminded me of something I did about
15 years ago. I had a pretty good relationship with a few fab vendors in
Southern California, and one slow week I asked them to provide me with
the FAB NOTES from lot of different customer's drawings. It was VERY
interesting to see how many variations there were, and to compare the
level of detail.
Maybe some rainy day we should ask everyone to send in their fab
note block (with any identifying text removed, of course) just to see
what people are doing out there. Would anyone be interested in that?
On 1/8/07, Sally Price <[log in to unmask]> wrote:
>
> Jack,
>
> Editing trace widths so the Fab house can hit controlled impedances, diff
> pairs, single ended traces and such is normal. That is acceptable, but,
> shaving pads and changing clearances is unacceptable. We call out on the
> layer stack up the plotted trace widths and the required impedances needed
> . Then in the Notes we added the note below:
>
> * ARTWORK SHALL NOT BE MODIFIED WITHOUT PRIOR CONSENT.
>
> * ALL REWORK MUST ADHERE TO IPC REWORKING IMPEDANCE CONTROLLED
>
> TRACES MUST HAVE PRIOR AUTHORIZATION FROM NVISION. (We found
> this to be troublesome also once the boards were finished and had problems,
> so I slipped this note in too!)
>
>
>
> This way it allows the Fab Shop to do what is necessary for impedance but
> forces a phone call/email on other modifications.
>
> I feel this method is the best of both and holds the Fab Shop accountable
> for any modifications that were not re-authorized.
>
> That is my two-cent worth.
>
> Sally Price
>
> Sally Price
>
> Senior PCB Designer
>
> 125 Crown Point Ct.
>
> Grass Valley, CA 95945
>
> Phone: (530) 265-1049
>
> FAX: (530) 265-1055
>
> e-mail: [log in to unmask]
>
> -----Original Message-----
> From: DesignerCouncil [mailto:[log in to unmask]<[log in to unmask]>]
> On Behalf Of Jack Olson
> Sent: Saturday, January 06, 2007 8:55 AM
> To: [log in to unmask]
> Subject: [DC] CAM Guy Gone Wild!
>
> A friend of mine (not on this list) asked me what I would do
>
> about something, and I didn't know (can you imagine that?)
>
> He is experiencing horrible problems with a product that
>
> should have worked as designed, only to discover that the
>
> CAM guy in China went crazy with editing! It took WEEKS
>
> to discover what he had done.
>
> The original design was primarily 5/5mil traces/clearances
>
> and this guy increased the plan clearances under BGAs to
>
> 10 for some reason, claiming "More Manufacturable". He
>
> also did all kinds of weird pad shaving and stuff which is
>
> mysterious but probably irrelevent. The poblem was that
>
> under the BGAs the added clearance took away return path
>
> for signals and I think even isoalted portions of ground from
>
> each other, and now the board won't even boot up!
>
> Now, I know many of you are gonna say you don't let vendors
>
> edit data, and even add notes to the drawing to prevent it.
>
> I'm not one of those people. We use several different vendors
>
> and if we want 5 mil traces and one vendor knows that their
>
> process consistently over-etches traces and they want to
>
> beef them up to 5.5 knowing that the end result will be 5,
>
> FINE!
>
> I am very happy when a vendor knows what to do to
>
> give me what I want. I actually DEPEND on them to edit
>
> whatever they need to give me my 50 ohm impedance, rather
>
> than forcing me to specify seperate sets of detailed con-
>
> structions to suit each of our appoved vendors. Since our
>
> products last 20 years or more, I don't even know WHO will
>
> be building them in the year 2020, so I DEPEND on them
>
> to do what is necessary to make the reliable product.
>
> That said, where do you draw the line between edits to give
>
> the desired results, and some "wanna be a designer" CAM
>
> guy making all kinds of "improvements"?
>
> What should I tell my friend to do about these very expensive
>
> boards that don't work?
>
> Jack
>
>
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